Solid-state modular microwave system



United States Patent [72] inventor DoyleS.Granberry Dallas, Tex.

[21] Appl. No. 628,140

[22] Filed Apr. 3, 1967 [45] Patented Dec. 22, 1970 [73 Assignee Texas Instruments Incorporated Dallas, Tex. a corporation of Delaware [5 4] SOLID-STATE MODULAR MICROWAVE SYSTEM Primary Examiner-Robert K. Schaefer Assistant ExaminerD. Smith, Jr.

Attorneys-Samuel M. Mims, Jr., James 0. Dixon, Andrew M. Hassell, Harold Levine, Jack A. Kanz, Kenneth R. Glaser, Gerald B. Epstein, Henry K. Woodward, Robert J. Crawford and Richards, Harris and Hubbard ABSTRACT: A solid-state, modular microwave transmitterreceiver assembly made up of a large number of transmitreceive modules each having an antenna. Each of the modules has functional electronic blocks mounted on both sides of a center mounting plate contained within a hermetically sealed package. The module packages generally conform to the center mounting plate and are elongated, with a greater width than thickness. The antenna extends from the front end of the module and connectors extend from the rear end. The connectors are plugged into a rear support structure and are retained in place by a series of retaining plates fastened by long screws to the rear support structure. The retaining plates also form the ground plane for the antenna array. The antennae are arrayed in horizontal rows and vertical columns, and the module packages are arranged in rows extending diagonally of the antenna rows and columns with the edges of the packages in each row abutting. A cooling fluid duct is formed between each adjacent pair of module rows by the walls of the module packages, the retaining plates and the rear support structure. A manifold and header assembly directs cooling fluid in opposite directions through alternate cooling fluid ducts. The antenna assembly of each module provides a hermetically sealed coupling between the antenna and the interior of the package, supports the dipole elements, and provides impedance and balun transforming. The functional electronic blocks are easily secured on the mounting plate by spot welded brackets and are replaceable. The hermetically sealed antenna assembly and coaxial input and output connections are connected to microstrip lines within the module by spot welded straps of solid ribbon or woven metal wire fabric, as are adjacent microstrip lines on adjacent abutting functional electronic blocks. Connections are made between functional electronic blocks on opposite faces of the mounting plate by a special coaxial structure extending through the mounting plate.

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INVENTOR DOYLE S. GRANBERRY ATTORNEY SOLID-STATE MODULAR MICROWAVE SYSTEM This invention relates generally to microwave transmitting and receiving, and more particularly relates to solid-state microwave antenna arrays.

While the specific embodiment of the invention described herein is an airborne terrain-following radar, this invention is equally applicable to other radar systems, such as those used for ground mapping, search and detection, fire control, tracking and navigation, as well as to microwave transmitting and receiving generally.

Radar systems in general, and airborne radar systems in particular, have long required considerable servicing and have been somewhat unreliable because of the many mechanical parts, such as rotary joints, motors, synchros, gears and other servo components normally essential to scanning the system, and the magnetrons used for transmitting, Klystrons used for transmitting and local oscillator service, and the high power transrnit-receive (TR) protection devices, for example. It is also difficult to achieve high power at higher frequencies and the electronic components mentioned tend to be more unreliable and less practical as the frequency of the transmitted and received energy increases.

In copending applications Ser. No. 397,519, filed Sept. 18, 1964, now U.S. Pat. No. 3,454,945, entitled Modular Integrated Electronics Radar, filed on behalf of Tom M. Hyltin, Ser. No. 397,472, filed Sept. 18, 1964, now U.S. Pat. No. 3,345,631, entitled Phased Array Radar Antenna Scan Control, filed on behalf of Leo A. Chamberlin, Jr., and Ser. No. 397,491, filed Sept. 18, 1964, now abandoned, entitled Integrated Circuit Modular Radar Antenna, filed on behalf of Harry F. Cooke, et al., all of which were filed on Sept. 18, 1964 and are assigned to the assignee of the present invention, a radar system is described which utilizes a large array of solidstate modules. Each module is substantially a complete microwave transmitter and receiver. Each module includes the necessary circuitry for amplifying relatively low RF carrier energy applied simultaneously to all of the modules, and multiplying the frequency to a higher frequency for transmission from the antenna. Each module also includes circuitry for processing high frequency energy received by the antenna to produce a lower frequency IF signal, which is also preamplified. In addition, each module includes phase shifting means for both the transmitted and the received energy so that the beam from the fixed antenna array can be electronically scanned. Although an X-band module transmitting at 9 GHz (9 X cycles per second) typically has a transmitting power of only about 1 watt, when a very large number of the modules transmit simultaneously, the total transmitting power is essentially the sum of the power of all of the modules. Arrays having on the order of thousands of modules are practical.

In order to operate at high frequencies, the individual antennae of the array must be spaced about one-half wavelength apart, which for X-band systems means that the antennae are arrayed in horizontal rows and vertical columns with about 0.7 inch spacing between the rows and columns. As a result, the frontal area of each module must be confined to a square about 0.7 inch on a side. Also, it is highly desirable to locate the electronic components as close to the antenna as possible, particularly the circuits operating at the higher frequencies. Merely obtaining sufficient space within the module to mount all the functional hybrid or integrated circuits, even though the circuits are highly microminiaturized, is a serious problem. Since very large numbers of modules are required, it will be appreciated that a very large number of relatively high power devices must be packed into a minimum volume, making it difficult to provide adequate cooling.

Also, there are very real problems associated with supplying high frequency signals to the module, transferring the high frequency signals between the various functional circuits within the module, transferring high frequency energy between the externally mounted radiating element and the internal circuitry, and getting the high frequency signals out of the module while maintaining the module hermetically sealed. Because of the number of components, it is also very desirable to be able to replace malfunctioning components during fabrication, rather than lose the entire module.

This invention is concerned with the structure of the array and individual modules required in order to achieve high component density and adequate cooling, economical fabrication costs, low maintenance requirements, and long service life. This is achieved by orienting the modules in spaced rows to form cooling fluid ducts between each two adjacent rows of modules. The rows of modules are preferably disposed diagonally of the rows and columns of antennae so that each module can have a maximum width, and thus maximum circuit mounting area for a given spacing between the antennae. The mounting area for the circuits is further increased by a package having a mounting plate extending between midpoints of a peripheral wall with the solid-state functional electronic components mounted on both sides of the mounting plate and hermetically sealed by a pair of lids. Support means for securing the modules in position in the array also forms the ground plane for the antenna array, and also two opposite walls of the cooling fluid ducts, and achieves this without obstructions within the cooling fluid ducts.

The invention is further concerned with an antenna assembly which mechanically supports a dipole in the proper position, transfers the RF energy through the wall of the hermetically sealed module package, and provides the necessary impedance and balun transformation between the internal transmission line and the radiating elements.

The invention is also concerned with a means for mounting the functional electronic blocks on the mounting plate of the module package, interconnecting functional electronic blocks mounted on the same side of the mounting plate, interconnecting fiinctional electronic blocks mounted on opposite sides of the mounting plate, and interconnecting the blocks and hermetically sealed conductors extending through the wall of the package.

The novel features believed characteristic of this invention are set forth in the appended claims. The invention itself, however, as well as other objects and advantages thereof, may best be understood by reference to the following detailed description of illustrative embodiments, when read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a front perspective view of a microwave antenna array in accordance with the present invention;

FIG. 2 is an enlarged front view of a portion of the antenna array of FIG. 1;

FIG. 3 is an exploded perspective view of the parts missing from the structure illustrated in FIG. 2;

FIG. 4 is a sectional view taken substantially on lines 4-4 of FIG. 2;

FIG. 5 is a sectional view taken substantially on lines 5-5 of FIG. 2;

FIG. 6 is an isometric view of an RF module of the array of FIG. 1;

FIG. 7 is a side view of the module of FIG. 6;

FIG. 8 is a sectional view taken substantially on lines 8-8 of FIG. 7;

FIG. 9 is an edge view of the module of FIG. 6;

FIG. 10 is a front end view of the module of FIG. 6;

FIG. 11 is a rear end view of the module of FIG. 6;

FIG. 12 is a somewhat schematic front view of the antenna array of FIG. 1 with a portion of the structure removed to better illustrate certain aspects of the invention;

FIG. 13 is a side view of the structure shown in FIG. 12;

FIG. 14 is a rear view of the structure shown in FIG. 12;

FIG. 15 is a somewhat schematic layout of the functional integrated and hybrid circuits mounted in one half of the module of FIG. 6;

FIG. 16 is a somewhat schematic layout of the functional integrated and hybrid circuits mounted in the other half of the module of FIG. 6;

FIG. 17 is a sectional view taken substantially on lines 17-17 of FIG. 16;

FIG. 18 is a perspective view of the antenna assembly of the module of FIG. 6;

FIG. 19 is a sectional view taken substantially on lines 19-19 ofFIG. 18;

FIG. 20 is an enlarged view of a portion of FIG. 19;

FIG. 21 is a sectional view taken substantially on lines 21-21 of FIG. 20;

FIGS. 22A and 22B are somewhat schematic isometric views illustrating alternative means for mounting the integrated and hybrid circuits within the module of FIG. 6;

FIG. 23 is a somewhat schematic isometric view illustrating how the microwave circuits on adjacent substrates may be interconnected; and

FIG. 24 is a sectional view illustrating the manner in which the microwave circuits formed on substrates mounted in the different compartments of the module of FIG. 6 may be interconnected.

Referring now to the drawings, a microwave antenna array constructed in accordance with the present invention is indicated generally by the reference numeral 10. The particular antenna array 10 herein described and illustrated is a solidstate, electronically scanned airborne radar system of the type described in the above-referenced U.S. patent applications. In such a system, a very large number of very small modules 12, as shown in FIG. 6, are assembled in an array with the antennae of the modules disposed in a common plane. Each of the modules is essentially a separate microwave transmitterreceiver which includes solid-state circuitry for amplifying a relatively low frequency RF carrier signal, which can be more easily handled, then multiplying the frequency of the RF signal several times before it is radiated from the antenna during a transmit cycle. During the receive cycle, the high frequency RF signal is mixed with a local oscillator signal to produce an IF signal which is amplified before leaving the module. In addition, each module contains phase shift circuitry for both the transmit and receive cycles in order to electronically scan the beam from the fixed antenna array. For other applications, however, such as microwave relay applications, the modules may only transmit, or only receive, or may not utilize the phase shift networks for beam steering. This invention is concerned primarily with the structure of the modules rather than the electronic function of the modules.

Each of the modules 12 has a metal package with opposite front and rear end walls 14 and 16 which define a length, opposite edge walls 18 and 20 which define a width, and opposite side walls 22 and 24 which define a thickness. The opposite end walls 14 and 16 and opposite edge walls 18 and 20 are integrally formed and are of the same height, the height corresponding essentially to the thickness of the module package. A center mounting plate 26 extends between midpoints of the opposite edge walls 18 and 20 and the opposite end walls 14 and 16 and is preferably integral with the side walls to achieve the best possible heat transfer between the mounting plate and the walls. Walls 14, 16, 18 and 20 provide a continuous wall which extends around the periphery of the center mounting plate 26, is normal to the plate 26 and extends beyond both of the opposite surfaces of the plate 26, thus forming an integral body having a pair of oppositely facing, open topped chambers indicated generally by the reference numerals 28 and 30. The chambers 28 and 30 are hermetically sealed by lids 32 and 34 which may be stitch welded or soldered around their entire periphery to the edges of the walls 14, 16, 18 and 20. The two lids 32 and 34 and the four walls14, 16, 18 and 20 then form a hermetically sealed package.

An antenna assembly, indicated generally by the reference numeral 40, extends through and projects from the front wall 14 and is hermetically sealed therewith. A pair of hermetically sealed coaxial connectors 42 and 44 extend through and project from the rear end wall 16 to provide high frequency connections to the circuits located within chambers 28 and 30 and are also hermetically sealed. The connectors 42 and 44 are the male halves of a conventional plug-in type connector. Similarly, eight low frequency or DC male connectors 46 extend through a ceramic block 48 and provide DC connections to the interior of the module. The ceramic block 48 is hermetically sealed to the end wall 16 and is hermetically sealed around each of the connectors 46. It will be noted that one of the coaxial connectors and four of the DC connectors extend into each of the chambers 28 and 30. An indexing pin 50 also protrudes from rear end wall 16 to insure that the otherwise symmetrical package is inserted in the proper manner in the female receptacle for the connectors 42, 44 and 46. A pair of essentially semicircular grooves 52 and 54 extend the length of the edge walls 18 and 20, respectively. A forward facing, recessed shoulder 56 is formed around the periphery of the front face 14 by machining for purposes which will hereafter become evident.

Each of the modules 12 is plugged into a female receptacle carried by a rear support structure indicated generally by the reference numeral 60 in FIGS. 4 and 5. The rear support structure 60 includes a support plate 62 which is coextensive with the octagonal housing as illustrated in FIG. 12. At each position where a module 12 is to be plugged in, the support structure 60 provides a DC socket 64 for the eight low frequency connectors 46, a pair of female coaxial sockets 66 and 68 for the male coaxial connectors 42 and 44, and a bore 70 for the indexing pin 50. The DC sockets 64 are mounted on a DC wiring board 72 and extend through an opening in support plate 62 to a point essentially flush with the front face of plate 62. The coaxial sockets 66 and 68 are mounted on an RF submanifold 74 and extend through the DC wiring board 72 and partially through the support plate 62.

When the modules 12 are plugged into the sockets carried by support structure 60, the modules are arrayed as illustrated in FIGS. 2 and 12. It will be noted from FIG. 2 that the antenna assemblies 40 are arrayed in orthogonally disposed horizontal rows and vertical columns with the center-to-center spacing approximately one-half wavelength, which at 9 GHz is approximately 0.7 inch. However, the modules 12 are arrayed in rows extending diagonally of the rows and columns of the antenna assemblies 40, and are disposed in substantially edge abutting relationship as best seen in FIG. 12. Since the width of each module is substantially greater than the thickness, the rows of modules 12 are spaced apart and the side walls of the modules in each adjacent pair of rows form the opposite side walls of cooling fluid ducts a and 80b. The ducts 80a and 80b are identical but are designated by different reference characters for purposes which will hereafter become more evident.

The modules 12 are secured in place in their respective sockets by means of a plurality of H-shaped clamp plates 82, as best shown in FIG. 3. Each plate 82 is formed from metal and has an electrically conductive sealing gasket 84 over its rear face. The total thickness of each plate 82 is equal to the distance the shoulder 56 is recessed from the front surface of the front end wall 14. Each plate 82 has a narrow center sec tion 82a which is adapted to fit over the shoulders 56 at the adjacent ends of two adjacent modules. A relatively long screw 86 passes through each center section 82a and extends back through the passageway formed by the adjacent semicircular grooves 52 and 54 of the two adjacent modules and is threaded into the support plate 62, as shown in FIGS. 4 and 5. The ends 82b of the plates 82 extend over the adjacent ducts 80a and 80b and engage the shoulders 56 of the modules in the two adjacent rows. Thus, a single plate 82 engages and secures four modules in place, and conversely each module is secured in place by four plates and four screws. Edges 82c of the plates extend into engagement with the corresponding edges 820 of the adjacent plates so that the combination of plates 82 provides a complete front wall for the cooling fluid ducts. It will be noted that plates 82 and the support plate 62 form the other two opposite side walls of the cooling fluid ducts 80a and 80b. The gasket material 84 prevents excessive leakage of the cooling fluid. In addition, the front surfaces of the plates 82 are coplanar with the from surfaces of the end walls 14 and the combined surface acts as the ground plane for the antenna array. The conductive gasket material 84 insures good electrical contact between the platesand the modules.

Referring once again to FIGS. 12, 13 and M, a cooling fluid header 88a supplies cooling fluid, typically ambient air, under pressure to ducts dlla through inlet ports i'tla, and exhausts cooling fluid from ducts hhb through exhaust ports 92a. Similarly, a header 88b supplies cooling fluid under pressure to ducts 80b through input ports hill) and exhausts the cooling fluid from ducts 3th: through exhaust ports 92a. The ports QPZ and 92a and WI) and 925; are formed by plates @511 and 9511 which extend between the rear support plate till and a front plate M (see FIG. 13) which is coplanar with the retainer plates $2 (see FIG. 3) and which therefore provides a continuation of the ground plane. Mounting holes 3 are provided in plate 9 3 to support the device. Plates 97 and 99 may extend around the remaining peripheries of plates 60 and Q 5. A pair of manifolds @641 and 96b extend around the rear surface of the rear support plate 60. Manifold Qua communicates with inlet ports 94M through openings 9811 in plate 6%, and manifold tib communicates with inlet ports 9% through openings 98!; in plate dd.

Thus, it will be noted that cooling fluid passes through manifold 96a, openings 98c, input ports 96a, ducts dlla, and exhausts through ports 92a, and passes through manifold 96!), openings 9%, input ports 9%, ducts hill), and exits through exhaust ports 9219. As a result, the cooling fluid flows in opposite directions in the ducts on either side of any one row of modules B2. The modules 12 adjacent the headers 8hr: and 88b will therefore have relatively cool fluid flowing by one face and relatively warm fluid flowing by the other face, while the modules generally centered between the headers will have cooling fluid at an intermediate temperature flowing over both faces. As a result, the net cooling effect upon all modules is substantially the same so that all modules are maintained at substantially the same temperature.

The antenna assembly 46 is illustrated in detail in FIGS. l8 and w. The antenna assembly 40 is comprised of a tubular sleeve 150, a center conductor 152, a ceramic disc 154, and a pair of antenna elements E56 and M 3. The ceramic disc 154 is hermetically sealed within the end of the tubular sleeve 150 and also around the end of the center conductor 152 by vacuum-tight hard solder seals. The diameter of the input portion 152a of the center conductor is selected relative to the diameter of the adjacent portion of the tubular sleeve 150 so as to provide a coaxial transmission line having a 50 ohm characteristic impedance. The center conductor has portions i525: and 1520 of enlarged diameter for transforming the 50 ohm characteristic impedance to the complex impedance required by the radiating elements 156 and when positioned in the antenna array. The sleeve 150 is split into halves 15th and 115612 to provide a balun transformation from the unbalanced coaxial transmission system to the balanced transmission system required to feed energy to the radiating elements l56 and 158. The slits M0 which separate the sleeve 15% into halves are approximately one quarter wavelength long. Antenna element 156 is secured in one of the sleeve halves 15% by a hard solder connection, and antenna element 158 is simply a continuation of the center conductor 152, but is also connected in a slot 162 by a hard solder connection. The antenna elements 156 and 158 are disposed one quarter wavelength from the ground plane. Thus, the antenna assembly 80 provides a hermetically sealed coaxial connection through the wall 14 of the module package, provides an impedance transformer for matching the standard 50 ohm characteristic input impedance of the rnicrostrip transmission of the internal circuit to the complex impedance required for the antenna, provides a balun transformer to convert from the unbalanced coaxial input to the balanced dipole antenna, and mechanically supports the radiating elements 1% and 1158 approximately one quarter wavelength above the surface of the end wall lid, which forms a portion of the ground plane for the antenna array.

The modules 12 may house, for example, the electronic circuitry described in copending US. Pat. application Ser. No. 606,427, tiled Dec. 30, i966, now abandoned entitled Transmit-Receive Module for X-Band Phased Array Radar System, filed on behalf of Tom M. l-lyltin and assigned to the assignee of the present invention. All of the functional blocks within the module are either hybrid circuits, in which case microstrip transmission lines and discrete semiconductor components are mounted on a ceramic substrate, or monolithic integrated circuits, in which case the active components are formed in a semiconductor substrate which also acts as the dielectric for the microstrip transmission lines. A typical layout for these circuits is shown in M68. 1'15-17.

During the transmit cycle a 2.25 Cilia carrier signal is applied through input coaxial connector 44 and is transferred by a strap W9 to a microstrip transmission line (not shown) on interconnector chip lid and through interconnection strap M2 to an S-band preamplifier 113. The output of the preamplifier 113 is coupled by strap lid to the input of a duplexer switch 115 which, during the transmit cycle, directs the signal through strap lid to a transmit phase shifter M7. The output of the transmit phase shifter l1 l7 is connected by strap 111% to a microstrip transmission line 115' on the receive multiplier 12%, which in turn is connected by strap T21 to microsn'ip transmission line M2 on an interconnect chip L23. Line 3122 is coupled by feed through connector 124 to a rnicrostrip transmission line 125 on micromodulator l3, and by strap 12'? to the input of a power amplifier 12%. The output of power amplifier 123 is connected by snap 129 to a transmit multiplier 13%, which increases the frequency to 9,0 Gblz. The RF frequency signal is then applied by strap R31 to a TR switch 132 which, during the transmit cycle, directs the energy to the center conductor 152 of the antenna assembly 4% by way of a strap connector 133.

During the receive cycle, a 2.125 Gl-iz signal is applied to input coaxial connector 4.4 and is passed through strap coupling 1 12 to the S-band preamplifier, strap coupling 1114 to the duplexer, and strap coupling 134 to a receive phase shifter 135. The output of the receive phase shifter is applied by strap coupling 136 to the receive multiplier 1120 which increases the frequency to 8.5 GHZ. The output of multiplier is connected by feed through connection 137 to a mixer 138. Also during the receive cycle, the TR switch connects the antenna to the mixer 138 where the 9.0 Gl-lz energy received by the antenna is mixed with the 8.5 Gllz local oscillator signal produced by multiplier 120 to derive a 500 MHZ IF signal. The IF signal is applied by way of strap connector 13% to IF pre amplifier 140. The output of the IF preamplifier is connected by strap connector ldl to a microstrip transmission line 142 on the micromodulator 126, which in turn is connected by strap connector M3 to a microstrip transmission line 1 54 on interconnector ship M5. The microstrip transmission line M4 is then connected to the output coaxial connector d2. by strap connector 1 56.

The micromodulator i226 produces the high current pulses defining the transmit cycle which are required to operate power amplifier iZS and switch duplexer M5 and TR switch 132. Choke M7 improves the operation of mixer 13%. A number of DC connections are illustrated on the drawings but will not be discussed in detail because they do not present an interconnection problem and are not an advance in the art. In general, the DC connections are made to the DC inputs 46 by ball bonded jumper wires and all connections between strip conductors on the various substrates can also be made by ball bonded jumper wires.

Since all circuits are mounted on the body of the package and interconnected to the antenna assembly of the various connectors before the lids $2 and 34 are sealed in place, the circuit can easily be tested after it is assembled. Because of the large number of functional blocks, it is highly desirable to be able to replace one or more faulty circuits after the entire module is assembled and tested, rather than discarding all of the circuits if any one circuit is bad. By mounting the circuits on the center mounting plate 26 using the bracket indicated generally by the reference numeral l'itl in Fit}. 122A, rather than by the conventional method of soldering the circuits in place, the faulty modules can be removed and replaced after the entire module has been tested as a unit.

The bracket 170 is comprised of a thin metal plate 172, 0.001 inch thick nickel foil, for example, which is substantially coextensive with the center mounting plate 26. A number of straps 17d are cut from the foil and bent upwardly as shown in dotted outline at l'lba. The straps ll'lb are located at points spaced around the peripheries of the various circuits, represented by circuit 174 in H6. 22A, to be mounted by the bracket 1170 Where it is desirable to place two circuits in closely abutting relationship, the straps 178 may be received in notches cut in the sides of the circuits, or may even extend through holes cut through the circuits. The straps Uh extend upwardly from the plate 1'72 a distance substantially greater than the thickness of the circuits to be mounted. A large number of tonguelike spring members i755 are also cut from the plate 172 and bent upwardly at an angle of approximately 45 or slightly less. The spring members 175 are disposed generally uniformly over the entire base plate 1'72. The base plate 172 is resistively spot welded to the mounting plate 26 at a number of points 176 generally spaced uniformly over its entire area.

The circuit l74i is placed in its proper position over the base plate W2 and between the appropriate straps 17%, then is forced downwardly to compress the spring members 17$ back into the plane of the base plate 72. The straps 1178 are then bent over metallized pads 177 on the surface of the circuit. The pads 17'! may be very thin vacuum deposited gold films, for example. The straps ll7b are then welded to the pads 1l7'7 using a split tip or gap resistance welder 11.79. The resulting weld is adequate to hold the circuit in place, but can be broken to remove a faulty circuit without damaging bracket l'l'il. The faulty circuit can then be replaced in the same manner.

The spring members E75 insure good thermal and electrical contact between the circuits and the mounting plate 26 because the springs bias the base plat against the mounting plate 26 and are themselves biased against the metallized ground plane on the bottom surface of the circuits.

An alternative method for securing the circuit in position on the bracket 170 is illustrated in FIG. 22B. Rather than bending the straps 178 over the edge of the circuit and welding it to the pads 177 as shown in FIG. 22A, a gusset Th1 may be welded to each of the straps. The gussets Mil may be formed from the same sheet material as the bracket 170. Each gusset has a first flange portion ltila which engages the top of the circuit and a second flange portion lblb which is disposed at a right angle to the first portion and is spot welded to the respective strap 17% at a point 182 above the top of the circuit. The welds 132 can also be broken to remove a faulty circuit without damaging bracket 170 and the circuit replaced.

The center conductor 152 of the antenna assembly all may be connected to the output of the TR switch 132 using the structure illustrated in FIGS. 20 and M. The center conductor 152 of the antenna assembly extends beyond the inner edge ll lla of the front end wall M and into a slot 119i formed in the center mounting plate 26. Since the center conductor 152 has a diameter approximately equal to the thickness of the mounting plate 26, the surface of the center conductor 152 is essentially coplanar with the surface of the mounting plate 26. However, the substrate on which the TR switch T32 is formed is almost as thick as the mounting plate 26 and is resting on the bracket 172. Therefore, the microstrip transmission line 192, which is the output of the TR switch and which extends to the edge of the substrate upon which the TR switch is formed, is not only spaced from the end of the center conductor M2, but is also spaced substantially above the plane of the center conductor. Thus, any interconnection between the coaxial transmission line and the microsuip transmission line will tend to create an impedance discontinuity due to the change from a ceramic dielectric to air and back to ceramic and due to the change in planes. Such an impedance discontinuity can reflect an intolerable amount of energy, particularly at 9 Gl-lz.

In accordance with this invention, however, the center conductor T52 can be connected to the microstrip transmission line 192 by a metal strap 133. The metal strap is preferably solid metal ribbon, but can also be woven wire mesh. The solid metal ribbon can be resistively welded to the coaxial center conductor Th2 and to the microstrip line 192. in order to compensate for the dielectric and geometric discontinuities of the interconnection, the width of the strap .lIiEl is increased to pro vide substantially the same characteristic impedance. For example, when connecting the coaxial transmission line from the antenna assembly 459, which has a 50 ohm characteristic impedance, to a microstrip transmission line, also having a 50 ohm characteristic impedance, the strap 1133 should be about 0.045 inch wide. This compares with a width of 0.020 inch required for the microstrip transmission line to provide a 50 ohm characteristic impedance when using a ceramic substrate 0.020 inch thick.

The woven wire fabric is not as mechanically stable as the solid metal ribbon, but has the advantage of being easily welded to the center conductor and to the strip transmission line using a heated tool having a very small tip to press the wire fabric against the center conductor and microstrip line.

lit will be noted from H68. 15 and lb that the entire surfaces of the mounting plate 245 are substmtially covered by functional circuit blocks and interconnector chips, the interconnector chips merely providing the microstrip transmission lines necessary to interconnect the circuits and the coaxial connectors extending through the end wall. The circuit blocks and interconnector chips all have the same thickness and a metallized ground plane on the bottom face. Microstrip transmission lines are formed by strip conductors on the top surface of the substrate and the ground plane. The characteristic impedance of the microstrip transmission lines is determined by the thickness and dielectric properties of the substrate material and the width of the strip conductors, and these variables are customarily selected to produce a transmission line having a 50 ohm characteristic impedance. Since all of the substrates have substantially the same thickness, the microstrip transmission lines carrying the high frequency signals can be interconnected by connector straps as described in connection with FlGS. l5 and 116. For example, connector strap 131 which connects the output of the transmit multiplier to the TR switch 132 may be formed as shown in FIG. 23. The microstrip transmission line 202 on the duplexer switch 132 extends to the edge of the circuit block. A microstrip transmission line 208 extends to the edge of the multiplier circuit block Bi) and is aligned with the microstrip transmission line are on the TR switch. A strap of gold wire mesh ilill bridges the gap between the adjacent circuit blocks and extends over the adjacent ends of the microstrip transmission lines 292 and 20%. The strap is welded to the transmission lines by using the tip of a heated tool to press the wire mesh against the respective microsttip transmission lines to form localized welds 2%. Alternatively, a solid metal ribbon may be substituted for the wire mesh strap and welded using the split tip resistive welder illustrated in FIG. 22A.

The dielectric discontinuity resulting from the change from a ceramic to air at the gap which must necessarily exist between the adjacent substrates may be compensated by increasing the width of the strap 131 in order to maintain the same characteristic impedance and thus eliminate impedance discontinuities which should reflect an intolerable amount of high frequency energy. However, for very close spacing between the circuit blocks, the strap may be the same width as the microstrip transmission lines.

in accordance with another aspect of this invention, the feed through connectors 124 and i3? (see H68. 15 and in), for example, may be constructed as shown in the detailed sectional view of FIG. 2d. A hole 226* is bored through the central mounting plate as. The bore 226? may be located immediately adjacent the edge of the two substrates to be connected, as illustrated by the relationship of the bore to substrate 222, or may pass through both substrates, as illustrated by the relationship of the bore to substrate 224, or may be a combination of the relationships as actually illustrated in FIG. 24. The substrates 222 and 22d may be mounted on the mounting plate 26 using the brackets l'7ll as illustrated. The microstrip transmission lines to be interconnected, for example strip line 226 on substrate 222 and strip line 22% on substrate 224, extend to points immediately adjacent the bore 220 An insulating sleeve 2%, preferably made of quartz, is coated with a metallized film 2311 around its mid portion, but is not coated adjacent the ends. The sleeve is then inserted in the bore 229. A wire conductor 232 passes through the insulating sleeve 23b and the opposite ends are flattened at 232.41 and 2321; until they are approximately the same width as the strip lines 226 and 22%. The ilat portions of the conductor 232 are bent over the strip lines and spot welded using an electric gap welder as previously described.

Using a trial and error procedure, the characteristic impedance of the feed through connector can be adjusted by varying the length of the metallized film 231 on the insulating sleeve 2%, or the diameter of wire 232 adjusted, until any impedance discontinuity is reduced to an acceptable level for a given installation.

Although preferred embodiments of the invention have been described in detail, it is to be understood that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

I claim:

1. in a microwave system, the combination of:

a plurality of RF modules, each module having opposite front and rear end walls;

an antenna assembly extending from the front end wall of each module having an antenna spaced from the front end wall;

electrical connector means disposed at the rear end wall;

a rear support assembly having an electrical connector means mating with the connector means on each module, the modules being arranged in a'plurality of spaced rows with the modules in each row disposed in adjacent relationship such that each two adjacent rows of modules form two opposite side walls of a cooling fluid duct with the rear support assembly forming the rear walls of the ducts; and

a plurality of retaining plate means engaging the modules adjacent the front end wall and each connected to the rear support assembly for retaining the modules in place, the retaining plate means engaging to form the front walls of the cooling fluid ducts.

2. The combination defined in claim 1 wherein: the antennae of the modules are arrayed in a common plane and the from surfaces of the retaining plate means form at least a part of a ground plane for the antenna array.

3. The combination defined in claim 1 wherein: each retaining plate means is connected to the rear support assembly by means extending between adjacent modules in the same row of modules.

4. The combination defined in claim 3 wherein:

each module has a forwardly facing shoulder formed at those edges of the front face that are disposed adjacent the two adjacent modules in the same row of modules;

each retaining plate extends over and engages the forwardly facing shoulders on two adjacent modules; and

each retaining plate is connected to the rear support plate by a screw passing through the retaining plate and between the modules and threaded into the rear support late.

5. %he combination defined in claim 4 wherein:

the antennae are arrayed in rows and columns, and the rows of modules are disposed diagonally of the rows and columns of antennae;

each module has a forwardly facing shoulder formed around the periphery of the front wall;

each retaining plate extends over the adjacent shoulder of the adjacent modules in the two adjacent rows of modules;

the retaining plates collectively form the front walls of the 5 cooling fluid ducts; and

the front surfaces of the retaining plates and the front surfaces of the from wells of the modules collectively form a continuous ground plane for the array of antennae.

6. The combination defined in claim l wherein each antenna assembly comprises:

a tubular sleeve hermetically sealed in a bore extending through the front wall of the module, the sleeve extending approximately onequarter wavelength from the front wall of the module and being split into generally semicircular halves for a length of approximately one quarter wavelength;

an antenna element electrically and mechanically connected to the front end of each half of the split sleeve;

a center conductor extending from a point within the module through the tubular sleeve and electrically connected to the front end of one of the halves of the split sleeve; and

a dielectric body hermetically sealed around the center conductor and within the tubular sleeve.

7. The combination defined in claim 6 wherein the diameter of the center conductor is varied to provide an impedance transformer matching the impedance of the coaxial transmission lines formed by the center conductor and the portion of the tubular sleeve passing through the front wall with the impedance of the antenna when disposed in the array of antennae.

3. The combination defined in claim l wherein each module comprises:

a hermetically sealed package having a mounting plate therein;

at least one functional circuit block comprised of solid-state circuit means formed on a substrate; and

means mounting the circuit block on the mounting plate comprising a thin metallic sheet having a planar base portion disposed between the circuit block and the mounting plate and a plurality of strap portions each disposed adjacent an edge of the circuit block and extending away from the base portion to a point beyond the circuit block, and a gusset connected to each strap at a point beyond the circuit block and extending over and engaging the surface of the circuit block to secure the circuit block in place on the mounting plate.

9. The combination defined in claim 8 wherein: each gusset is formed from a strip of metal sheet material bent to form first and second plate portions disposed at a right angle, the first plate portion engaging the upper surface of the circuit block and the second plate portion being welded to the respective strap at a point above the top surface of the circuit block.

ll). The combination defined in claim 8 wherein the base portion is further characterized by: a plurality of spring means spaced generally uniformly over the base portion for springingly engaging the undersurface of the circuit block to insure good heat transfer between the circuit block and the mounting plate.

ii. The combination defined in claim l wherein each module comprises:

a hermetically sealed package having a mounting plate therein;

at least one functional circuit block comprised of solid-state circuit means formed on a substrate; and

means mounting the circuit block on the mounting plate comprising a. thin metallic sheet having a planar base portion disposed between the circuit block and the mounting plate and a plurality of strap portions each extending from the base portion past an edge of the circuit block and over the circuit block to retain the circuit block in place on the mounting plate.

l2. The combination defined in claim ll wherein: each of the straps is bonded to the top surface of the circuit bioclt.

13. The combination defined in claim ll wherein: each of the straps extends over a metallized pad on the surface of the circuit block and is welded to the pad.

lid. The combination defined in claim ll wherein the base portion is further characterized by: a plurality of spring means spaced generally uniformly over the base portion for springingly engaging the undersurface of the circuit block to insure good heat transfer between the circuit block and the mounting plate.

15. The combination defined in claim l wherein:

each module comprises a hermetically sealed package having a mounting plate therein;

at least two circuit blocks mounted on the mounting plate, each circuit block being comprised of a circuit formed on a substrate at least partially comprised of rnicrostr'ip transmission lines formed by a metallized ground plane on the bottom surface of the substrate and a metal strip conductor of predetermined width on the top surface, the two substrates being mounted with the edges of the substrates in adjacent relationship and with the microstrip transmission lines extending to adjacent points at the adjacent edges of the substrates; and

a metal strap interconnecting the adjacent ends of the microstrip transmission lines, the width of the metal strap being selected to maintain substantially the same characteristic impedance as that of the microstrip transmission lines.

T6. The combination defined in claim 15 wherein: the metal strap is a length of woven wire fabric at least as wide as the microstrip transmission lines which overlaps each of the microstrip transmission lines and is bonded to each by at least one weld.

17. The combination defined in claim 15 wherein the metal strip is a length of solid metal ribbon having a width substantially greater than its thickness, and the ends of metal ribbon overlie the ends of the microstrip transmission lines and are bonded to each by at least one spot weld.

lb. The combination defined in claim 6 wherein:

each module comprises a hermetically sealed package having a mounting plate therein;

a TR circuit block mounted on the plate and disposed adjacent the end of the center conductor of the antenna assembly, the TR circuit having a microstrip transmission line formed by a metallized ground plane on the bottom side of the substrate and a strip conductor on the top side of the substrate, the microstrip transmission line extending to the edge of the substrate adjacent said center conductor; and v a metal strap interconnecting the center conductor and the microstrip transmission line, the metal strap having a width selected to maintain substantially the same characteristic impedance as that of the internship transmission line and the coaxial conductor formed by the center conductor and the tubular sleeve of the antenna assembly.

19. The combination defined in claim ill wherein: the metal strap is at least as wide as the microstrip transmission line.

Ztl. The combination defined in claim ll wherein each module comprises:

a package having a mounting plate extending between midpoints of the front and rear walls;

a circuit block mounted on each of the opposite faces of the mounting plate;

a bore extending through the mounting plate and disposed adjacent an edge of each circuit block;

a tubular insulating sleeve disposed in the bore;

a metallic film coating the outer surface of the tubular insulating sleeve, the metallic film terminating before reaching the surface of the respective circuit block that is remote from the mounting plate;

a microstrip transmission line formed on each of the circuit blocks and terminating adjacent the bore; and

a cylindrical conductor extending through the insulating sleeve and having flattened ends bonded to the microstrip transmission lines on the circuit bloclrs; the length of the metallized film on the tubular sleeve, the

external diameter of the tubular sleeve, and the diameter of the conductor being selected to substantially match the characteristic impedance of one of the microstrip transmission lines to the characteristic impedance of the other microstrip transmission line.

21. in a modular electronic system, the combination of:

a plurality of modules each having opposite front and rear walls;

electrical connector means disposed at'the rear end wall;

a rear support assembly having an electrical connector means mating with the connector means on each module, the modules being arranged in abutting relationship in a plurality of spaced rows such that each two adjacent rows of modules form two opposite side walls of a cooling fluid duct with the rear support assembly forming the rear walls of the ducts; and

a plurality of retaining plate means engaging the modules adjacent the front end wall and each connected to the rear support assembly for retaining the modules in place, the retaining plates engaging to form the front walls of the cooling fluid ducts.

22. The combination defined in claim 21 wherein: each retaining plate means is connected to the rear support assembly by means extending between two modules in the same row of modules. 

